Sally Floyd has a good page on CBQ, including her original papers. None of
it is Linux specific, but it does a fair job discussing the theory and uses
of CBQ.
Very technical stuff, but good reading for those so inclined.

Differentiated Services on Linux

This document by Werner Almesberger, Jamal Hadi Salim and Alexey
Kuznetsov describes DiffServ facilities in the Linux kernel, amongst which
are TBF, GRED, the DSMARK qdisc and the tcindex classifier.

Yet another HOWTO, this time in Polish! You can copy/paste command lines
however, they work just the same in every language. The author is
cooperating with us and may soon author sections of this HOWTO.

>From the helpful folks of Cisco who have the laudable habit of putting
their documentation online. Cisco syntax is different but the concepts are
the same, except that we can do more and do it without routers the price of
cars :-)

Stef Coene is busy convincing his boss to sell Linux support, and so he is
experimenting a lot, especially with managing bandwidth. His site has a lot
of practical information, examples, tests and also points out some CBQ/tc bugs.

TCP/IP Illustrated, volume 1, W. Richard Stevens, ISBN 0-201-63346-9

Required reading if you truly want to understand TCP/IP. Entertaining as
well.